Conventionally, in the gasoline engines equipped to automobiles, etc., direct injection gasoline engines have been employed from the viewpoint of improvements in fuel economy, etc. However, since particular matter (hereinafter referred to as “PM”) is generated by these direct injection gasoline engines, research into technology providing an exhaust purification filter (Gasoline Particulate Filter (hereinafter referred to as “GPF”) which captures PM in the exhaust passage of a gasoline engine has been progressing, accompanying the strengthening of emission laws in recent years.
In addition, a three-way catalyst (hereinafter referred to as “TWC”) which purifies CO, HC and NOx contained in exhaust gas is provided in a state loaded on a honeycomb carrier, in the exhaust passage of a gasoline engine. Particularly in recent years, a plurality of TWCs has been arranged in series in the exhaust passage in order to satisfy the required purification performance. For this reason, in addition to this plurality of TWCs, it is preferable to newly provide a GPF in the exhaust passage from the viewpoint of pressure loss and cost.
Therefore, technology has been proposed which loads TWC on the GPF to impart the three-way purification function to the GPF in addition to the PM capturing function (for example, refer to Patent Document 1). According to this technology, it is said to be possible to overcome the problems in pressure loss and cost, by integrating the GPF and TWC.
Patent Document 1: Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2013-50085